8342826: Improve performance of oopDesc::klass() after JDK-8305895

Reviewed-by: coleenp, shade, mli

src/hotspot/share/oops/objLayout.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "oops/markWord.hpp"
+#include "oops/objLayout.hpp"
+#include "runtime/globals.hpp"
+#include "utilities/debug.hpp"
+
+ObjLayout::Mode ObjLayout::_klass_mode = ObjLayout::Undefined;
+int ObjLayout::_oop_base_offset_in_bytes = 0;
+bool ObjLayout::_oop_has_klass_gap = false;
+
+void ObjLayout::initialize() {
+  assert(_klass_mode == Undefined, "ObjLayout initialized twice");
+  if (UseCompactObjectHeaders) {
+    _klass_mode = Compact;
+    _oop_base_offset_in_bytes = sizeof(markWord);
+    _oop_has_klass_gap = false;
+  } else if (UseCompressedClassPointers) {
+    _klass_mode = Compressed;
+    _oop_base_offset_in_bytes = sizeof(markWord) + sizeof(narrowKlass);
+    _oop_has_klass_gap = true;
+  } else {
+    _klass_mode = Uncompressed;
+    _oop_base_offset_in_bytes = sizeof(markWord) + sizeof(Klass*);
+    _oop_has_klass_gap = false;
+  }
+}

src/hotspot/share/oops/objLayout.hpp

@@ -0,0 +1,66 @@
+/*
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_OOPS_OBJLAYOUT_HPP
+#define SHARE_OOPS_OBJLAYOUT_HPP
+
+/*
+ * This class helps to avoid loading more than one flag in some
+ * operations that require checking UseCompressedClassPointers,
+ * UseCompactObjectHeaders and possibly more.
+ *
+ * This is important on some performance critical paths, e.g. where
+ * the Klass* is accessed frequently, especially by GC oop iterators
+ * and stack-trace builders.
+ */
+class ObjLayout {
+public:
+  enum Mode {
+    // +UseCompactObjectHeaders (implies +UseCompressedClassPointers)
+    Compact,
+    // +UseCompressedClassPointers (-UseCompactObjectHeaders)
+    Compressed,
+    // -UseCompressedClassPointers (-UseCompactObjectHeaders)
+    Uncompressed,
+    // Not yet initialized
+    Undefined
+  };
+
+private:
+  static Mode _klass_mode;
+  static int  _oop_base_offset_in_bytes;
+  static bool _oop_has_klass_gap;
+
+public:
+  static void initialize();
+  static inline Mode klass_mode();
+  static inline int oop_base_offset_in_bytes() {
+    return _oop_base_offset_in_bytes;
+  }
+  static inline bool oop_has_klass_gap() {
+    return _oop_has_klass_gap;
+  }
+};
+
+#endif // SHARE_OOPS_OBJLAYOUT_HPP

src/hotspot/share/oops/objLayout.inline.hpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_OOPS_OBJLAYOUT_INLINE_HPP
+#define SHARE_OOPS_OBJLAYOUT_INLINE_HPP
+
+#include "oops/objLayout.hpp"
+
+inline ObjLayout::Mode ObjLayout::klass_mode() {
+#ifdef ASSERT
+  assert(_klass_mode != Undefined, "KlassMode not yet initialized");
+  if (UseCompactObjectHeaders) {
+    assert(_klass_mode == Compact, "Klass mode does not match flags");
+  } else if (UseCompressedClassPointers) {
+    assert(_klass_mode == Compressed, "Klass mode does not match flags");
+  } else {
+    assert(_klass_mode == Uncompressed, "Klass mode does not match flags");
+  }
+#endif
+#ifdef _LP64
+  return _klass_mode;
+#else
+  return Uncompressed;
+#endif
+}
+
+#endif // SHARE_OOPS_OBJLAYOUT_INLINE_HPP

src/hotspot/share/oops/oop.cpp

@@ -152,10 +152,6 @@ bool oopDesc::is_array_noinline()       const { return is_array();       }
 bool oopDesc::is_objArray_noinline()    const { return is_objArray();    }
 bool oopDesc::is_typeArray_noinline()   const { return is_typeArray();   }
 
-bool oopDesc::has_klass_gap() {
-  return UseCompressedClassPointers && !UseCompactObjectHeaders;
-}
-
 #if INCLUDE_CDS_JAVA_HEAP
 void oopDesc::set_narrow_klass(narrowKlass nk) {
   assert(CDSConfig::is_dumping_heap(), "Used by CDS only. Do not abuse!");

src/hotspot/share/oops/oop.hpp

@@ -31,6 +31,7 @@
 #include "oops/accessDecorators.hpp"
 #include "oops/markWord.hpp"
 #include "oops/metadata.hpp"
+#include "oops/objLayout.hpp"
 #include "runtime/atomic.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/macros.hpp"
@@ -324,7 +325,9 @@ class oopDesc {
   inline bool mark_must_be_preserved() const;
   inline bool mark_must_be_preserved(markWord m) const;
 
-  static bool has_klass_gap();
+  inline static bool has_klass_gap() {
+    return ObjLayout::oop_has_klass_gap();
+  }
 
   // for code generation
   static int mark_offset_in_bytes()      { return (int)offset_of(oopDesc, _mark); }
@@ -346,15 +349,7 @@ class oopDesc {
   }
 
   static int base_offset_in_bytes() {
-    if (UseCompactObjectHeaders) {
-      // With compact headers, the Klass* field is not used for the Klass*
-      // and is used for the object fields instead.
-      return sizeof(markWord);
-    } else if (UseCompressedClassPointers) {
-      return sizeof(markWord) + sizeof(narrowKlass);
-    } else {
-      return sizeof(markWord) + sizeof(Klass*);
-    }
+    return ObjLayout::oop_base_offset_in_bytes();
   }
 
   // for error reporting

src/hotspot/share/oops/oop.inline.hpp

@@ -34,6 +34,7 @@
 #include "oops/arrayOop.hpp"
 #include "oops/compressedKlass.inline.hpp"
 #include "oops/instanceKlass.hpp"
+#include "oops/objLayout.inline.hpp"
 #include "oops/markWord.inline.hpp"
 #include "oops/oopsHierarchy.hpp"
 #include "runtime/atomic.hpp"
@@ -95,43 +96,48 @@ void oopDesc::init_mark() {
 }
 
 Klass* oopDesc::klass() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass();
-  } else if (UseCompressedClassPointers) {
-     return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (ObjLayout::klass_mode()) {
+    case ObjLayout::Compact:
+      return mark().klass();
+    case ObjLayout::Compressed:
+      return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 
 Klass* oopDesc::klass_or_null() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass_or_null();
-  } else if (UseCompressedClassPointers) {
-    return CompressedKlassPointers::decode(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (ObjLayout::klass_mode()) {
+    case ObjLayout::Compact:
+      return mark().klass_or_null();
+    case ObjLayout::Compressed:
+      return CompressedKlassPointers::decode(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 
 Klass* oopDesc::klass_or_null_acquire() const {
-  if (UseCompactObjectHeaders) {
-    return mark_acquire().klass();
-  } else if (UseCompressedClassPointers) {
-    narrowKlass narrow_klass = Atomic::load_acquire(&_metadata._compressed_klass);
-    return CompressedKlassPointers::decode(narrow_klass);
-  } else {
-    return Atomic::load_acquire(&_metadata._klass);
+  switch (ObjLayout::klass_mode()) {
+    case ObjLayout::Compact:
+      return mark_acquire().klass();
+    case ObjLayout::Compressed: {
+      narrowKlass narrow_klass = Atomic::load_acquire(&_metadata._compressed_klass);
+      return CompressedKlassPointers::decode(narrow_klass);
+    }
+    default:
+      return Atomic::load_acquire(&_metadata._klass);
   }
 }
 
 Klass* oopDesc::klass_without_asserts() const {
-  if (UseCompactObjectHeaders) {
-    return mark().klass_without_asserts();
-  } else if (UseCompressedClassPointers) {
-    return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
-  } else {
-    return _metadata._klass;
+  switch (ObjLayout::klass_mode()) {
+    case ObjLayout::Compact:
+      return mark().klass_without_asserts();
+    case ObjLayout::Compressed:
+      return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
+    default:
+      return _metadata._klass;
   }
 }
 

src/hotspot/share/runtime/arguments.cpp

@@ -46,6 +46,7 @@
 #include "nmt/nmtCommon.hpp"
 #include "oops/compressedKlass.hpp"
 #include "oops/instanceKlass.hpp"
+#include "oops/objLayout.hpp"
 #include "oops/oop.inline.hpp"
 #include "prims/jvmtiAgentList.hpp"
 #include "prims/jvmtiExport.hpp"
@@ -3673,6 +3674,7 @@ jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
   if (UseCompactObjectHeaders && !UseCompressedClassPointers) {
     FLAG_SET_DEFAULT(UseCompressedClassPointers, true);
   }
+  ObjLayout::initialize();
 #endif
 
   return JNI_OK;